442 SLASH

Ok, so yesterday i bought a JCM 800 B ( 16 ohm input ) cab to complete my vintage modern stack and im rather confused because on the back of the Vintage Modern head it has an out put selection of 8 or 16 ohms and my 1960A cab has a selection between mono( 8 ohm input ) and stereo( 16 ohm input ). when using the mono seting on the cab all 4 speakers are in use but seems to be robbing the b cab of all its power, but when using the srtereo setting it only uses two speakers and gives the JCM800 B cab abit more power, so any and all help to this confusion would be appreciated, thanks in advance, jeff.

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Bieling3

You can run them with the head set on 8hm stereo and both cabs (of course ones hardwired so you don't have to worry) set to 16ohm. I believe...

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442 SLASH

the bottom cab is from 83, and it only has a 16 ohm input so i dont know if that effects any thing

MKB

Actually this behavior is correct. Your top cab, when set to mono, is 8 ohms. The bottom cab is 16 ohms. When both are connected, the 8 ohm cab will draw around twice the power of the 16 ohm cab, and will be louder. However, when the top cab is set to stereo, it is at 16 ohms (2 speakers in use), and draws the same power as the bottom cab, so the volumes are more balanced.

I'm afraid there really isn't a way to use both cabs in mono and balance the power out, as the speakers in the mono/stereo cab are most likely 8 ohms each, while the ones in the bottom cab are 16 ohms.

442 SLASH

Thanks MKB

Bieling3

Is he not supposed to set both cabs to 16 ohm and the head to 8 ohm stereo? This is what I've been told here on the forum numerous times.

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Salsg

If the stereo cab is standard wiring and speakers, then stereo mode is 8 ohm, and mono mode is 4 or 16 ohm.

Run it in 16 ohm mode (mono) and also your other cab (16 ohm) and set you head to 8 ohm.


Their could be several reasons for a perceived loss in power for the B cab. One is the A cab is closer to your ears, so it will sound louder and cut thru more. Stand 15'+ back and see.

Another reason is the speaker sensitivity. The A cab looks like it has the 75s, what speakers does the B cab have?

Third thing it could be are speakers out of phase?

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442 SLASH

thanks guys, i had a buddy of mine come over and set it all up for me